ｃｈｅｍ~~

Question

Oxygen sample obtained from Artic has a relative atomic number 15.994 whereas another sample from the Antartica has a relative atomic number of 16.
Why is there a difference in these values?

relative atomic MASS 先岩...(not relative atomic number )

打錯~~~

Answer 1

Relative atomic mass of oxygen is the weighted average of the relative isotopic masses for all isotopes of oxygen. Oxygen has three natural-occurring isotopes 16O, 17O and 18O with relative isotopic masses 15.944, 16.999 and 17.999 respectively.

Since the abundance of different isotopes of oxygen (i.e. mole ratio of 16O, 17O and 18O) in Artic and that in Antarctica are not the same (slightly different), the relative atomic masses (i.e. the weighted average isotopic masses of 16O, 17O and 18O) are slightly different.

Answer 2

因為以前是以氫(H)為量度相對原子質量的基準(其相對原子質量為1.00.....),但隨後用碳(C)為相對原子質量的基準(其相對原子質量為12正(可能因為有很多個有效數字而本人並不清楚,所以寫正))可能因為用碳為相對原子質量的誤差較低,所以其相對原子質量會有些微變化.

2007-09-25 13:38:34 補充：
1.00.......是本人看化學書得悉氫的小數點後2或者3個位後有1-9的數,但本人忘記了數值是多少;而碳的相對原子質量應是12.00000............(在大多數化學書是這樣寫的,但是沒有省略號)